Traveling wave tube



Oct. 21, 1958 w. KLEIN ET AL 2,357,547

. TRAVELING WAVE TUBE Filed April 4, 1955 2 Sheets-Sheet 1 IHH INVENTORS W. KLEIN" W. FRIZ ATTORNEY Oct. 21, 1958 w. KLEIN ETAL 2,857,547

TRAVELING WAVE TUBE 2 Sheets-Sheet 2 Filed April 4. 1955 RN wN mvsmons W KLEIN- W FRIZ ATTORNEY United States Patent TRAVELING WAVE TUBE Werner Klein, Korntal, and Walter Friz, Stuttgart, Germany, assignors to International Standard Electric Corporation, New York, N. Y., a corporation of Delaware Application April 4, 1955, Serial No. 499,163 Claims priority, application Germany April 3, 1954 6 Claims. (Cl. 315-35) Traveling wave tubes consist of a beam generating system, of a retardation line and of a collector. For the proper functioning of the traveling wave tube it is important that the axis of the gun system (beam generating system), of theretardation line and of the collector are adapted to each other with a sufficient accuracy, whereby also the high frequency requirements, e. g. the prevention of. a feedback, have to be considered. Up to now various arrangements have become known for achieving the afore said aim: Y

The invention will be better understood from the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, in which:

Figs. '1 and 2 are diagrammatic illustrations of prior art tube constructions;

Fig.3 is a diagrammatic illustration of a unitary assembly for traveling wave tubes in accordance with this invention;

Fig. 4 is a detailed fragmentary cross-sectional'view of a .traveling wave tube structure incorporating the features of this invention, and

Fig. 4a is a cross-sectional 4-4 of' Figure 4. v e

Fig. 1 of the accompanying drawings shows'an embodiment in which the vacuum tube takes over the task of mutually holding the system components. To this end the vacuum tube 1 is enlarged in its diameter in the zone of the gun system 2. The gun system is retained in position on the one side by a tight fitting disk 5 and is supported on the other side in the adjoining narrowed helix holding section of the vacuum tube by means' of a tightfitting helix terminating cylinder 6. In this case the retardation line is constituted by the wire helix 3, which is held in positionbetween thediel'ectric rods 7. Instead of the dielectric rodsthere alsohave been used dielectric pipes as holding arrangements for the helix. The collector-sided end of the helix is likewise retained in positionby; meansof a second cylinder 6a on'the side of the collector 4. In this arrangement it is of a disadvantage that the vacuum tube takes over the holding of the system view made along the line and that further the exact axis-true position ofthe thick I and the thin glass section requires a rather difficult. glass processing. Furthermore, also the'method of holding the helix with the aid of a dielectric pipe bears various disadvantages. Besides the influence of the dielectric upon the phase velocity of the wave on ,the retardation line there still appears a weakening effect of the coupling between wave and beam which is due to the distortion of the electromagnetic field towards theholding arrangement. This causes a reductionof the amplification and, in the case of power tubes, also a reduction'of the maxihigh-fr equency output power. The unavoidable 'loss factor of the dielectric, in addition causes'an attenuation of the retardation line, which increases the aforesaid effect. Effects are being made, therefore, to provide, if

2,857,547 P atented 0 21, 1958 2 possible, only a spot-shaped-contacfing of the helix with the dielectric, e. g. with the aid of holding rods.

Fig. -2fshows a typeof embodiment in which the difficulty of the glass processing has been reduced insofar as there is employeda vacuum tube 8 with a constantly calibrated internal diameter. The system components (gun system 9 and helix section 10) which are fitted into this glass container, as a matter of fact, have one common axis. However, in the demand for an exact accuracy to size with respectto the built-in components, there is also to be found its'weakest point, because the mounting requires a verygreat care and the inside of the glass container can easily be injuredor damaged during the assembly, which maybe the cause of forthcoming cracks in theglass container. a V

Fig. 3 shows an arrangement in which the vacuum tube onlyserves as an envelope andin which the gun system and the helix section form a self-supporting structural respect to high frequency. The gun system, especially in the case of powertubes, has a certain minimum diameter which determines the smallest possible tube diam-j eter in this .type of embodiment. The tubes are provided with waveguide couplings The coupling-in and coupling .and coupling-out waveguide, the cut-off frequency of out waveguides must therebyzbe' joined by a metal-pipefor providing a rigid connection and holding. This pipe, however, represents an unwanted transmission path having a high-pass filter character between the coupling-in which mayeasily fall Wifllllllhe range of the electronic amplification. This cut-oft frequencyincreases with a' decreasing hollow pipe diameter-.1. Hence in these types. a of embodiment therehave to be provided additional means for excluding the unwanted transmission path, which may: easily be the causeof: a feedback. In accordance with the invention it is suggested, therefore, to employ a pipe as supporting means between the helix holding at the input-and at the outputwaveguide within the vacuum tube. The diameter-of this pipe preventing the formation the said feedback. This arrangement will now be particularly described with reference to an exemplified embodiment.

Fig. 4 of the accompanying drawings shows an arrangement according'to the invention. The gun system 15 is held' in a coaxialposition with respect to the glass tube 27 by meansof aring 16. A pot-shaped metal cylinder 17, forming "the cathode-sided termination of the high frequency circuit, is slipped over the gun system 15. With the aid of the metallic connecting component 19 the pot-shaped metal cylinder 17 is in a rigid connection with thepot-shaped metal cylinder 18. The said connecting,

circuitzla of the tube there are arranged accordingly the pot-shaped metalcomp'onents 17d and 18a together with the metallic connecting'component 19a. The helix 22 is supported inside three dielectric rods 23, the respective pe ition of each of which is secured on the side of the In addition thereto, the embodiments of Figs. 2 and 3 bear disadvantages with collectorby means of the collecting part 24a. This component 24a isrigidly connected'withthepot-shaped metal cylinder 17a. In the same manner the helix is fixed by means of the ceramic rods inside the pot 17 with the aid of'the collecting part 24; The connection of the structural group; at the input-waveguide '21, with" the structural group at the output waveguide 211: is established with the aid of a dielectric pipe (e. g. of ceramics ofglass) 25'. This pipe of dielectric material" is providedon both ends with flanges 26 and 26a which are rigidly joined to the pots 18 and 18a- (e. g. by hard soldering). The second supporting point of the self-supporting tube system is represented by the collector 28 sealed to" the other end of the vacuum-tube; The pot17a-rests-onthe collector-bymeans of a disk of dielectric material 295 The pipe 25- helix is. nov longer possible owing to the smaller diameter of .the pipe within the operatingrange of the tube.- It' will-.be of advantage tocarry out: the dimensioning. of the pipe diameter according to the following high frequencypoints of view: The diameter. of the pipe is supposed to be sosmall that: the longest possible waveguide wavelengthin the space between the helix and the holding-pipe is beyond: the shortest amplified wave. On: the other hand the diameter of the pipe is. not toubechosen so small that its dielectricwill. start to havev a' substantial influence uponthe, helix waveform, With; the aid 'of these conditions, the vfollowing limits. maybe set up with respect to the diameter dnOf'l'hGndiGlfiCfl'iC pipe:

whereby U represents the optimum DI CI operating voltage in volts and 7\ the optimum operating wavelength in the same units as d It is-assumed thereby, that the electronic"amplifieationrange of the tube extendsover' approximatelyone octave.-- Coaxial wave propagation is effectively suppressed by'the-attenuating-layeronthe dielectric pipe. f coursethi's attenuatinglayer may also be pplied to the inside,-. or toith'e'outside and the inside of thendielectn'c piper The spaoe 'b'etween'the 'dielectriepipe and the case. wall 3lgrepresents a st-ronglya't tenuated' coaxial line, the :attenuation'of' which 'is suffi-E cient for suppressing. a coaxial wave for the feedback excitation, By means of this arrangement for the suppression of waveguide waves there is provided agreater freedom in the, selection:ofiithe'diameter-of the vacuum tube which may now depend: on: the points I of view a re-' gardingthe dimensioningofthe gum system;- For further increasing the attenuation 'of tthecspacezbetweenthe pipe and the case wall the inside; and/or the outside-wall of the vacuum tube-may 'be 'provi'ded iwith an attenuationcoating. The elimination of the feedback path by means of the conventional insertion of suppression 'elements 'is not as effective as the, WidebEDddbSS attenuation described hereinbefore, becausethe; said isuppression elementsare' selective. Of course, there: are-1 .provid edf attenuating means within the retardation. line order-tosuppress a self -excitation by the fundamentalihelixiwaveform. 1 i

The construction of'the'coupling zone .with'the metallic connecting part 19 is .particularlynshown in Fig. 4a off thedrawingsn The metallic-connectingpart: '19 may e. g'-. have the :shape of a kidney? and; when; beingrembodiedas a'hollow. part, enablesthe-leading= througlicoffurther" connecting, leads, e. g. fora tubecomprisingapluralityiof" helix or helices within the. vacuumwcont i r :,7

4 a side of the power supply. Likewise the connecting part may consist'ofan arrangement comprising a plurality of rods or small pipes. In this arrangement, at the same time, all elements which are required for the transformation, e. g. the components 17, 18 and 20, in particular the component 19, are placed inside the pipe. By this there may be achieved a coupling of the helix to the. output circuits in a manner which is independent on the position. Thearrangement of the rigid connectiomofl the pot-shaped components 17 and 18 bymeans, of/the part 19 bears the furthenadvantage accordingtowhi'ch. the connecting pipe 25 does not project into thewaveguide zone 21 or 21a respectively, thus avoiding additional transformer losses .from'the helixto' .the. waveguide caused by the losses in the dielectric.

While we havedescribed above" the principles of our invention in connection with specific apparatus, it is to. be clearly understood that this description is madeonly by wayof example and not as a limitation to the scope, of our invention as set forth in the objects thereof and. in-the accompanying claims.

Whatis claimed is:

l. A traveli'ng wave' tube comprisinga helicalv delay. line, relativelyrigid supportingmeans for supporting said T. line throughout its length; .a tube of dielectric material; supported incoaxial spaced relationship with said helix and extendi'ngalong the helix to within a short distance of each end thereof, said dielectric tube having a diameter d complying'with' the limitation expressed by:

where U is the optimum-D. C. operating voltage involts and A is the optimum operating wavelength of' the travel-' ing. waventube in the same units as d anattenuating coating provided on said dielectric-tube;andan evacuated envelope enclosing said helix and tube.

2.1 A traveling wavetube according-to claim *1, wherein:said attenuation coating ison 'the inner and-outer sur-' face of said tube.

3'. A-traveling wave tube according to 'claim'l, further comprising coupling members at each endof said" tube and positioned within said. envelope-for providing-coupling to. external wave guides; said= tube-being-firm1y-; 7

attached. at its opposite ends'to respective-of said"cou= pling members. 1

4: A. traveling. wave tube as. claimed in 'cl'a'im'i; char-i .acterised. in that each of th'e: couplingmembers-consists" of two 1 cup-shaped cylinders, anda metallic supportingmember; rigidly .inter-connecting said' cylinders; 5. Atravelihg-wave tube according'to claim 4; further comprising an: electron gunpositioned at one end' of" said; helical line. for directing an electron beam therealong, and Ia collector: electrode atthe other end of'said-i helical line for. collecting the electrons of said beams," means for supporting'one of saidcup-shapedmembers on'said collectorelectrode, and means for mounting-said electron. gun. in thefother of 'said'cup-shaped members;

6., A traveling-wave tube accordingtoclaim 5, further comprising-a ringmember on. said gun member-for-sup porting the gun,:end of said assemblywithin said envelopeand a member on said collector electrode sealed? with said envelope.

References Cited in the file of this patent 

